The invention relates to automatic and semi-automatic welding systems for butt welding sections of flat stock into relatively large unitary panels, and for applying stiffener webs to such panels.
In fabricating relatively large, stiffener reinforced panels from thin metal stock, the required welding operations entail a number of difficult part-holding tasks, primarily because of material shrinkage associated with the localized heating and subsequent cooling of the welded areas. For example, in the manufacture of reinforced panel sections for the hull and decks of a lightweight metal ship, made of aluminum, it is not uncommon to incur substantial wastage of materials and parts due to permanent and excessive distortion exhibited in completed subassemblies that has resulted from localized expansion and subsequent shrinkage of material adjacent butt welded seams, and adjacent fillet welds that join stiffener webs to the panel.
Heretofore, the only practical solution to these problems has been to carfully and manually tack weld the various workpieces together, and then employ special purpose jigs and tooling to constrain the parts to the proper position during the completion of manually performed butt and fillet welding operations. Preliminary tack welding followed by manual strength welding has been found not only very time consuming and inefficient, but also the cause of many irregularities and defects in the completed welds. Moreover, the special purpose tooling and jigs, required by the nature of the manual welding operations, are not universally usable with different workpiece configurations, and thus it has been necessary for the manufacturer to build and maintain numerous and widely varied tools and jig assemblies to match the size and shape of each of the particular panel/stiffener subassembly.
Accordingly, one object of the invention is to provide an apparatus, suitable for use in conjunction with an automatic or semi-automatic welding system, for holding workpieces that are to be joined by welding in a way that eliminates distortion in the completed assembly, which would otherwise occur as the result of localized expansion and subsequent shrinkage of material during the welding operations.
Another object is to provide in an automatic or semi-automatic welding system, method and apparatus for welding together flat stock into relatively larger unitary panels by a sequence of butt welding operations wherein the sections of flat stock are held in place during automatic or semi-automatic welding in such a way as to eliminate warpage or other distortion of the completed panel.
Additionally, it is an object of the invention to provide method and apparatus, for use in conjunction with an automatic or semi-automatic welding system, for placing, positioning, holding and welding a stiffener web to a workpiece panel and to accomplish these tasks in a way that produces a completed subassembly of a reinforced panel structure that is substantially free of permanent distortion which would otherwise result from successive expansion and shrinkage of the panel and stiffener which unavoidably occurs during the welding operation.